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Do birds sleep with their eyes closed?

on 15th May 2010

In the earlier post on sleeping birds, Lena Chow brought up the subject of sleep in birds.

In all except one of the birds she encountered during her night trip down the Menanggul tributary, they were “sleeping with their eyes open. The Blue-eared Kingfisher (Halcyon capensis) was ‘blinking’ once in a while, but otherwise had its eyes fully open. Despite their eyes being open, I think they were not conscious of our presence as we approached within touching distance and torches were shone at them,” recounted Lena. The one she believes to be sleeping with its eyes closed was one of the two White-chested Babblers (Trichastoma rostratum) that was curled up into a furry ball.

According to Gill (2006), “Birds typically close their eyes when they sleep, but just one eye at a time for unihemispheric sleep. Unihemispheric sleep enables continued vigilance.” This type of sleep is termed slow-wave sleep or SWF and “requires the use of one side of the brain at a time, a primary feature of bird sleep.”

There is another type of sleep, the rapid-movement sleep, or REM, as seen in mammals. Here, both eyes are closed. In birds, very short and frequent bouts of REM sleep are common. Those swifts and terns that sleep on the wing indulge in “Quick bouts of REM sleep combined with (one-eyed) unihemispheric sleep”.

And birds also dream – but that is another story…

Image of the Stork-billed Kingfisher (Halcyon capensis), with its eyes fully open is by Lena Chow.

Reference:
Gill, F. B., 2007. Ornithology. W. H. Freeman & Co., New York. 758 pp.

If you like this post please tap on the Like button at the left bottom of page. Any views and opinions expressed in this article are solely those of the authors/contributors, and are not endorsed by the Lee Kong Chian Natural History Museum (LKCNHM, NUS) or its affiliated institutions. Readers are encouraged to use their discretion before making any decisions or judgements based on the information presented.

YC Wee

Dr Wee played a significant role as a green advocate in Singapore through his extensive involvement in various organizations and committees: as Secretary and Chairman for the Malayan Nature Society (Singapore Branch), and with the Nature Society (Singapore) as founding President (1978-1995). He has also served in the Nature Reserve Board (1987-1989), Nature Reserves Committee (1990-1996), National Council on the Environment/Singapore Environment Council (1992-1996), Work-Group on Nature Conservation (1992) and Inter-Varsity Council on the Environment (1995-1997). He is Patron of the Singapore Gardening Society and was appointed Honorary Museum Associate of the Lee Kong Chian Natural History Museum (LKCNHM) in 2012. In 2005, Dr Wee started the Bird Ecology Study Group. With more than 6,000 entries, the website has become a valuable resource consulted by students, birdwatchers and researchers locally and internationally. The views and opinions expressed in this article are his own, and do not represent those of LKCNHM, the National University of Singapore or its affiliated institutions.

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